d. attié, p. colas, giganon, i. giomataris, v. lepeltier, m. was

[email protected] TPC Jamboree, Aachen – March 2007 1

D. Attié, P. Colas, A. Giganon, I. Giomataris,

B. V. Lepeltier, M. Was

Gain measurement in Gain measurement in

various gas mixtures and various gas mixtures and

optimization of the optimization of the

stabilitystability

TPC Jamboree, Aachen 14-16 March 2007TPC Jamboree, Aachen 14-16 March 2007


•Systematic measurements to provide gain curves

•Simulations using GARFIELD/Magboltz

•Comparisons between measurements and simulations for gain curves

•How to optimize the detector stability for ILC-TPC ?

Overview


• Micromegas is a parallel plate gas avalanche detector with a small gap

• Micromesh held by pillars 50 m above the anode plane

Micromegas: gas amplification system

Edrift = 100-1kV/cm

Eamp = 50k-100 kV/cm

Micromesh

Drift electrode

Am

plifi

cati

on

gap ~

50

mC

onvers

ion

gap ~

13 m

m

― Pillars ―

Charge particle

Pads


Setup

Description:

• Transparent plastic box of 23 cm x 23cm x 8 cm size

• “Standard” 50 m mesh of 10 cm x 10 cm size

• Sources: - Fe 55 (5.9 keV) - COOL-X (8.1 keV)

• Monitoring of: - pressure - H2O

• Gas mixing system with triple mixture available

Goals:

• find gas mixture comfortable gain margin to use into a Micromegas TPC• know as much as possible the maximum gain (to avoid spark)


Gain measurements : simulation

Edrift ~ 220 V/cm

Longitudinal diffusion

Transversal diffusion

Drift Velocitiy

Simulations from GARFIELD/MAGBOLTZ




Choice : Edrift = 150 V/cm




Choice : Edrift = 300 V/cm


100

1000

10000

100000

50 55 60 65 70 75 80 85 90 95 100

Field (kV/cm/atm)

Ga

in

Iso : 1%

Iso : 2%

Iso : 3%

Iso : 4%

Iso : 5%

CF4 : 3%, Iso : 1%

CF4 : 3%, Iso : 2%

CF4 : 3%, Iso : 3%

CH4 : 6%

CH4 : 7,5%

CH4 : 9%

CH4 : 10%

CH4 : 5%, CF4 : 3%

CH4 : 5%, CF4 : 5%

CH4 : 5%, CF4: 10%

CH4 : 10%, CF4 : 3%

CH4 : 5%, CO2 : 3%

CH4 : 10%, CO2 : 10%

CO2 : 10%

CO2 : 20%

CO2 : 30%

CO2 : 10%, Iso 2%

CO2 : 10%, Iso 5%

CO2 : 10%, Iso 10%

CF4 : 3%, CO2 : 1%

CF4 : 3%, CO2 : 3%

CF4 : 3%, CO2 : 5%

Iso : 2%, CH4 : 10%

Iso : 5%, CH4 : 10%

Iso : 10%, CH4 : 10%

Ethane 10%

Ethane 5%

Ethane 3,5%

Ethane 2%

Ethane 3,5% - CO2 10%

Ethane 3,5% - CF4 3%

Ethane 3,5% - CF4 10%

Ethane 3,5% - Iso 2%

Mixtures of gases containing argon: gain curves

iC4H10

Cold gases: CO2, CH4

C2H6

Micromegas Mesh : 50 m gap of 10x10 cm² size


5%

10%

15%

20%

25%

30%

35%

40%

100 1000 10000 100000 1000000

Gain

RM

S

Iso : 1%

Iso : 2%

Iso : 3%

Iso : 4%

Iso : 5%

Resolution vs. gain

Argon/Isobutane

• Best RMS for a gain between 3.103 & 6.103

• Degradation increase in inverse proportion to the quencher


100

1000

10000

100000

50 55 60 65 70 75 80 85 90 95 100

Field (kV/cm/atm)

Ga

in

Iso : 1%

Iso : 2%

Iso : 3%

Iso : 4%

Iso : 5%

CF4 : 3%, Iso : 1%

CF4 : 3%, Iso : 2%

CF4 : 3%, Iso : 3%

CH4 : 6%

CH4 : 7,5%

CH4 : 9%

CH4 : 10%

CH4 : 5%, CF4 : 3%

CH4 : 5%, CF4 : 5%

CH4 : 5%, CF4: 10%

CH4 : 10%, CF4 : 3%

CH4 : 5%, CO2 : 3%

CH4 : 10%, CO2 : 10%

CO2 : 10%

CO2 : 20%

CO2 : 30%

CO2 : 10%, Iso 2%

CO2 : 10%, Iso 5%

CO2 : 10%, Iso 10%

CF4 : 3%, CO2 : 1%

CF4 : 3%, CO2 : 3%

CF4 : 3%, CO2 : 5%

Iso : 2%, CH4 : 10%

Iso : 5%, CH4 : 10%

Iso : 10%, CH4 : 10%

Ethane 10%

Ethane 5%

Ethane 3,5%

Ethane 2%

Ethane 3,5% - CO2 10%

Ethane 3,5% - CF4 3%

Ethane 3,5% - CF4 10%

Ethane 3,5% - Iso 2%

Mixtures of gases containing argon: gain curves

Micromegas Mesh : 50 m gap of 10x10 cm² size


• Rose-Korff approximation:

= P×A×e-B(P/E)

A, B: constants to be determined in measurements

Only applicable to fields E << 100 kV/cm.

The Townsend coefficient

• We assumes homogeneous field gain vs. amplification gap d:

G(d) = ed = (E)

is calculated by Magboltz

• But, in reality field could not be very homogeneous, not for very small gaps (i.e. high field) = (E(z))

G(d) = e[E(z)]dz


Townsend coefficients measurements

G = N/N0 = exp[×d]

With = A×P×exp[-B×P/E]

Argon-Isobutane

B = 90,767

B = 89,1

B = 87,1

B = 90,2

B = 109,7

B = 121,4

6,8

6,9

7,0

7,1

7,2

7,3

7,4

7,5

7,6

7,7

0,01 0,011 0,012 0,013 0,014 0,015 0,016 0,017 0,018 0,019 0,02

P/E

Ln(a

lpha

)

Iso : 5%

Iso : 4%

Iso : 3%

Iso : 2%

Iso : 1%

CH4 : 10%

Linéaire (Iso: 5%)Linéaire (Iso: 4%)Linéaire (Iso: 3%)Linéaire (Iso: 2%)Linéaire (Iso: 1%)Linéaire(CH4 : 10%)


Ar/CH4 mixtures: measurements

10

100

1000

10000

100000

50000 55000 60000 65000 70000 75000 80000 85000 90000 95000 100000E/P (V/cm/atm)

Gai

n

ArCH4 10% : Mea.

ArCH4 9% : Mea.

ArCH4 7,5% : Mea.

ArCH4 6% : Mea.

ArCH4 10% : Sim

ArCH4 9% : Sim

ArCH4 7,5% : Sim

ArCH4 6% : Sim

G < 104


Ar/CH4: simulation vs. measurements

10

100

1000

10000

100000

50000 55000 60000 65000 70000 75000 80000 85000 90000 95000 100000E/P (V/cm/atm)

Gai

n

ArCH4 10% : Mea.

ArCH4 9% : Mea.

ArCH4 7,5% : Mea.

ArCH4 6% : Mea.

ArCH4 10% : Sim

ArCH4 9% : Sim

ArCH4 7,5% : Sim

ArCH4 6% : Sim

Good agreement:measurements are Consistent with simulations,


Ar/CO2 mixtures: measurements

10

100

1000

10000

100000

50000 55000 60000 65000 70000 75000 80000 85000 90000 95000 100000

E/P (V/cm/atm)

Ga

in

ArCO2 10%

ArCO2 20%

ArCO2 30%

ArCO2 10% : Sim.

ArCO2 20% : Sim.

ArCO2 30% : Sim.

G ~ 2.103


Ar/CO2: simulation vs. measurements

10

100

1000

10000

100000

50000 55000 60000 65000 70000 75000 80000 85000 90000 95000 100000

E/P (V/cm/atm)

Ga

in

ArCO2 10% : Mea.

ArCO2 20% : Mea.

ArCO2 30% : Mea.

ArCO2 10% : Sim.

ArCO2 20% : Sim.

ArCO2 30% : Sim.

Agreement with the slopebut not with the absolute gain


100

1000

10000

60 65 70 75 80 85 90

E/P (kV/cm/atm)

Ga

in

TDR

TDR Simu

TDR: Ar/CH4/CO2 (92:5:3)

G < 3.103


100

1000

10000

60 65 70 75 80 85 90

E/P (kV/cm/atm)

Ga

in

TDR

TDR Simu

TDR: Ar/CH4/CO2 (92:5:3)


Ar/C2H6: simulation vs. measurements :

10

100

1000

10000

100000

50000 55000 60000 65000 70000 75000 80000 85000 90000 95000 100000

E/P (V/cm/atm)

Ga

in

ArEth 2% : Mea.

ArEth 3,5% : Mea.

ArEth 5% : Mea.

ArEth 10% : Mea.

ArEth 2% : Sim

ArEth 3,5% : Sim

ArEth 5% : Sim

ArEth 10% : Sim

UV photons ?

G < 105


Ar/C2H6: simulation vs. measurements :

10

100

1000

10000

100000

50000 55000 60000 65000 70000 75000 80000 85000 90000 95000 100000

E/P (V/cm/atm)

Ga

in

ArEth 2% : Mea.

ArEth 3,5% : Mea.

ArEth 5% : Mea.

ArEth 10% : Mea.

ArEth 2% : Sim

ArEth 3,5% : Sim

ArEth 5% : Sim

ArEth 10% : Sim

Penning effect

UV photons ?

Agreement with the slope at low fields but not with the absolute gain and the photons effects


10

100

1000

10000

100000

1000000

50000 55000 60000 65000 70000 75000 80000 85000

E/P (V/cm/atm)

Gai

n

ArIso 1% : Mea.ArIso 2% : Mea.ArIso 3% : Mea.ArIso 4% : Mea.ArIso 5% : Mea.

Ar-CF4-Iso 1% : Mea.Ar-CF4-Iso 2% : Mea.Ar-CF4-Iso 3% : Mea.Ar-CF4-Iso 1% : SimAr-CF4-Iso 2% : SimAr-CF4-Iso 3% : Sim

Ar/iC4H10 mixtures: measurements

G ~ 105


Ar/iC4H10: simulation vs. measurements

10

100

1000

10000

100000

1000000

50000 55000 60000 65000 70000 75000 80000 85000

E/P (V/cm/atm)

Gai

n

ArIso 1% : Mea.ArIso 2% : Mea.ArIso 3% : Mea.ArIso 4% : Mea.ArIso 5% : Mea.ArIso 1% : SimArIso 2% : SimArIso 3% : SimArIso 4% : SimArIso 5% : SimAr-CF4-Iso 1% : Mea.Ar-CF4-Iso 2% : Mea.Ar-CF4-Iso 3% : Mea.Ar-CF4-Iso 1% : SimAr-CF4-Iso 2% : SimAr-CF4-Iso 3% : Sim

Agreement with the slope at low fields but not with the absolute gain and the photons effects


10

100

1000

10000

100000

1000000

50000 55000 60000 65000 70000 75000 80000 85000

E/P (V/cm/atm)

Gai

n

ArIso 1% : Mea.ArIso 2% : Mea.ArIso 3% : Mea.ArIso 4% : Mea.ArIso 5% : Mea.ArIso 1% : SimArIso 2% : SimArIso 3% : SimArIso 4% : SimArIso 5% : SimAr-CF4-Iso 1% : Mea.Ar-CF4-Iso 2% : Mea.Ar-CF4-Iso 3% : Mea.Ar-CF4-Iso 1% : SimAr-CF4-Iso 2% : SimAr-CF4-Iso 3% : Sim

Ar/iC4H10+ 3% CF4: simulation vs. measurements

+ 3% CF4


10

100

1000

10000

100000

1000000

50 55 60 65 70 75 80 85 90 95 100

E/P (kV/cm/atm)

Ga

in

Neon - Iso 5%

Neon - Iso 5% - Simu

Penning effect

The Penning mixture is a mixture of inert gas with another gas, that has lower ionization voltage than either of its constituents

Penning effect : Is a energy transfer from molecule A to molecule Bwhich have lower ionization potential than the first excited state of molecule A.


10

100

1000

10000

100000

1000000

50 55 60 65 70 75 80 85 90 95 100

E/P (kV/cm/atm)

Ga

in

Neon - Iso 5%


Neon - Iso 5% - Argon 1%

Neon - Iso 5% - Argon 1% - Simu

Penning effect

The Penning mixture is a mixture of inert gas with another gas, that has lower ionization voltage than either of its constituents

Penning effect : Is a energy transfer from molecule A to molecule Bwhich have lower ionization potential than the first excited state of molecule A.


10

100

1000

10000

100000

1000000

50 55 60 65 70 75 80 85 90 95 100

E/P (kV/cm/atm)

Ga

in

Neon - Iso 5%




Neon - Iso 5% - Argon 1,9%

Neon - Iso 5% - Argon 1,9% - Simu

Penning effect


10

100

1000

10000

100000

1000000

50 55 60 65 70 75 80 85 90 95 100

E/P (kV/cm/atm)

Ga

in

Neon - Iso 5%




Neon - Iso 5% - Argon 1,9%

Neon - Iso 5% - Argon 1,9% - Simu



Penning effect


Penning effect

GasIonization energy Ei

(eV)

Xe 12,1

Ar 15,7

Ne 21,6

He 24,5

Possibilities of Penning mixtures:

• Ne-Ar• Ar-Xe• Ar-Acetylene• Ne-Xe• Ar-impurities who have lower Ei ?!• …


Estimation of the gain

Gain depends on:

• Gas mixtures properties (Penning effect, ionization energies)• Detector geometry• Gas pressure• High voltage

• Simulation: suppose that the detector is perfect, pressure and high voltage stable and constant.

• Need to take care of Penning effect but the energy transfer from molecule A to molecule B in gases is not well simulated

• It may be possible to estimate this effect using the ionization P ioni and excitation Pexci probabilities extracted from MAGBOLTZ

• We suppose that a fraction of photons from molecule A deexcitation ionize molecule B with the measured probability of transfert Ptrans.

• For the Penning mixture, the Townsend coefficient α could be replaced by αeff:

ioni,B

exci,Atransferteff P

PPαα

• Pexci,A excitation probability for molecule A

• Pioni,B ionization probability for molecule B

• Pioni,B measured probability of transfert


Cross section of gas

Drift velocity and diffusion coefficients depend on the precision δ of the gas cross sections. This precision decreases with the complexity of the rotational and

vibrationalcross sections.

• He: δ < 0.5 %

• Ar, Xe, Ne: δ < 1 %

• Hydrocarbons with small nC (CH4, C2H6) : δ ~ 1 %

• CO2, CF4 : δ ~ 1-2 %

• iC4H10 : δ ~ 3 %

• Heavier gases: δ > 3 %


Conclusions

•Systematic measurements will help to choose and optimize the detector stability (best , low voltage) for ILC-TPC

•Simulations using Magboltz work well for drift velocities and diffusion

•But, need to add correction factor for the Townsend coefficient used for gain calculation


Pressure monitoring in Saclay

990

992

994

996

998

1000

1002

1004

1006

1008

1010

27/0

6/20

06

02/0

7/20

06

07/0

7/20

06

12/0

7/20

06

17/0

7/20

06

22/0

7/20

06

27/0

7/20

06

01/0

8/20

06

06/0

8/20

06

Pres

sure

(m

bar

)


Gain vs. amplification gap


• The resistive foil prevents charge accumulation, thus prevents sparks

• Gains higher than obtained with standard anodes can be reached

Micromegas gain

― Without resistive foil

― With resistive foil (current)

― Without resistive foil

― With resistive foil (current)

ArIso5%

d. attié, p. colas, giganon, i. giomataris, v. lepeltier, m. was

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